I drove on to C&W in Chantilly and discovered that they are closing at the end of February. Their Woodbridge store is staying open so they are still doing some limited buying. That meant they didn't take any of what I had. And, even with the store closing discount, their prices are still on the high side.
Finally, I went to Reston Used Book Shop, in the Lake Anne Village Center. I can't imagine why I've never been in there before. They bought all the rest of my paperback mysteries (3 of mine for one of theirs) and two of the other books I had. Their prices seem generally fair and they have an interesting enough assortment that I actually spent some money above what I had in trade.
There wasn't enough left to be worth going anywhere else. I do have two boxes ready to go to The Book Thing in Baltimore and sort of intended to do that on Sunday. But it was one of those days where I never made it out of my pajamas.
Total result was 27 books out, 13 in. At this rate, I might be able to fit everything on my shelves by 2074.